1. Field of the Invention
The invention refers to a process for melting scrap iron, pelletized sponge iron in pre-reduced condition and/or solid pig iron for the purpose of producing steel, in which process the melting heat is introduced into a charge contained in a receptacle, from below the charge by means of burners and the resulting liquid material discharged from the melting receptacle is collected in a ladle, in which there are, if required, performed further alloying steps.
2. Description of the Prior Art
From DE-AS 25 04 889 there has already become known a process for continuously melting scrap iron, iron sponge or the like, in which process a carburization of the bath should be achieved by adding to the charge big coal lumps of low reactivity below the oxidizing melting zone. On account of the oxidizing flame of usual fuel-oxygen-burners, the charged materials become oxidized in an undesired manner, and there were made several proposals to prevent such oxidation or to reduce at least the degree of such oxidation. In this connection, there has, for example, been proposed in AT-PS 363 503 to blow coal dust onto the bath together with the effluent gases of the combustion. When adding coal to the charge, there results, in particular, in shaft furnaces of high construction, most frequently the drawback that a considerable portion of the added coal is burned within the furnace shaft together with the flame gases and is, for this reason, only effective at a reduced degree within the melting area. Introducing carbon at the bottom of the melting receptacle, by blowing, for the purpose of carburizing the bath requires, as a rule, additional heating means within the area of the bottom. Carbon being blown into the bath results in a further desoxidation of the melt, which desoxidation may result in undesired excessive boiling reactions. Likewise, a relatively high degree of inhomogeneity possibly resulting in an excessive local boiling reaction may be observed within the bath when charging corresponding big coal lumps which subsequently shall pass through the melting zone and shall become effective within the bath.
It is in particular in case of melting furnaces of small size that the charge passes the furnace within a relatively short time interval. Within such a short time interval, no complete reaction of lumpy coal may be expected in contrast to the conditions existing, for example, within a blast furnace. A great portion of the equally supplied carbon, for example being supplied in the shape of coke, would rather scarcely be changed within the downwardly travelling column until the flame area and would be substantially burned within the flame burning by supplying oxygen.
With consideration of the excessive oxidation when using fuel-oxygen-burners, there was, as a rule, charged coal in the melting processes known up till now, and this for the purpose to keep low the iron losses resulting from a high content in iron oxides of the slag. A high content of the slag in iron oxides results in the additional drawback that such a relatively aggressive slag attacks the furnace cladding in an excessive degree and thus reduces the lifetime of the refractory cladding.